1. Field of the Invention
The present invention relates to a cylindrical lithium rechargeable battery, and more particularly, to a cylindrical lithium rechargeable battery including a core member having a short circuit preventing part to prevent electrode assembly short circuits.
2. Discussion of the Background
Recently, small and light-weight electronic devices such as cellular phones, notebook computers, and camcorders have been widely developed and manufactured. Such devices have built-in battery packs in order to operate without a separate power supply. The is built-in battery pack includes at least one battery for outputting a predetermined voltage to drive the portable electronic device for a predetermined time period.
The battery packs typically use rechargeable batteries for economical usage. For example, the rechargeable batteries may be nickel-cadmium (Ni—Cd) batteries, nickel-hydrogen (Ni-MH) batteries, and lithium batteries such as a lithium (Li) battery and a lithium ion (Li-ion) battery.
In particular, the lithium rechargeable battery's operating voltage (3.6V) may be about three times higher than that of the nickel-cadmium battery and the nickel-hydrogen battery, which are widely used in portable electronic devices. Further, the lithium rechargeable battery's energy density (energy per unit weight) is larger than that of the nickel-cadmium battery and the nickel-hydrogen battery. Therefore, usage of the lithium rechargeable battery has rapidly increased.
In a typical lithium rechargeable battery, a lithium oxide material is used as a positive electrode activation material, and a carbon material is used as a negative electrode activation material. Generally, a lithium rechargeable battery may be classified as a liquid electrolyte battery or a polymer electrolyte battery according to its electrolytic solution. Additionally, a lithium battery using a liquid electrolyte is typically called a lithium ion battery, and a lithium battery using a polymer electrolyte is typically called a lithium polymer battery. Furthermore, the lithium rechargeable batteries can be manufactured in various shapes. Representative shapes include a cylinder, a polygon, and a pouch.
The typical cylindrical lithium rechargeable battery includes an electrode assembly having a positive electrode plate coated with positive electrode activation material, a negative electrode plate coated with negative electrode activation material, and a separator interposed between the positive and negative electrode plates to prevent short circuits therebetween. These components are substantially cylindrically wound together and housed in a cylindrical case. An electrolyte solution is injected into the cylindrical case to allow lithium ion movement.
A cylindrical lithium rechargeable battery may be manufactured as follows.
First, the positive electrode plate, which is coated with positive electrode activation material and connected to a positive electrode tap, the negative electrode plate, which is coated with negative electrode activation material and connected to a negative electrode tap, and the separator are stacked. The stack is then wound in a substantially cylindrical shape, thereby completing the electrode assembly.
Next, the substantially cylindrical electrode assembly is placed in the cylindrical case, a process for preventing the electrode assembly from separating is performed, the electrolyte solution is injected into the cylindrical case, and the case is sealed.
In general, in the cylindrical lithium rechargeable battery, an empty space may be formed at a central portion of the electrode assembly. However, the empty space may allow the electrode assembly to unwind and deform.
A method of inserting a predetermined core member into the central space of the electrode assembly has been proposed to solve this problem.
FIG. 1 is a perspective view for explaining a conventional core member.
Referring to FIG. 1, the conventional core member 100 may be constructed in a shape of a pipe by winding a plate, where a cut 110 is formed along a longitudinal direction thereof.
The core member 100 may prevent a wound electrode assembly from unwinding. Additionally, the core member 100 may prevent the electrode assembly from being deformed due to external pressure. Namely, the core member 100 may also support the electrode assembly against external pressure.
However, if external pressure moves or deforms the core member 100, the electrode assembly, particularly the separator, may be damaged. More specifically, since upper and lower ends of the cut 110 formed along the longitudinal direction of the core member 100 may be sharp, the edge may pierce the electrode assembly, particularly, the separator, and damage the electrode assembly.
As described above, damage to the separator may cause a short circuit between the positive and negative electrode plates, so that the cylindrical lithium rechargeable battery may break or explode.
In order to solve the aforementioned problem, a core member 100 may be constructed by bending both ends of the cut 110 in an inward direction of the core member 110, as disclosed in Japanese Laid-open Application No. 03-092148.
However, when external pressure is exerted on the electrode assembly, the core member 100 may not adequately support the electrode assembly against the external pressure corresponding to the bended portions of both ends of the cut 110.